This invention relates to gas-liquid dispersion devices for increasing gas-liquid dispersion efficiency in gas-liquid contact between a gas and a liquid, or between a gas and a slurry, as well as to gas-liquid contact apparatus and wastewater treatment systems employing the gas-liquid dispersion devices.
Conventionally, gas-liquid contact apparatus are used in various industrial sectors and applications including chemical plants, plating facilities, food production facilities, pharmaceutical manufacturing facilities, pulp and paper manufacturing facilities, dyeing operation and dye manufacturing facilities, glass manufacturing facilities, power generating facilities, and photographic processing facilities. A gas-liquid contact apparatus of this kind is constructed such that a gas and a liquid are brought into mutual contact in a system, in which the liquid forms a continuous phase, to perform a chemical reaction, a heat exchange operation, dissipation, an absorption operation, and so on.
At an intake portion of the aforementioned gas-liquid contact apparatus, there is provided a gas-liquid dispersion device (also known as a distributor) which can sufficiently disperse the gas and liquid for improving gas-liquid contact efficiency. More particularly, the gas-liquid dispersion device is a device for dispersing the gas and/or liquid (or causing them to contact with each other in certain cases) at an intake portion of such containers as a reaction vessel, a bubble tower, a multitubular heat exchanger, and a packed tower.
Known examples of the aforementioned gas-liquid dispersion device used when a gas forms a continuous phase include a spray nozzle, a notch trough type device, and perforated plates with or without weirs, in which a liquid is dispersed downward. On the other hand, examples used when a liquid forms a continuous phase include a sparger ring mounted at a lower part of a reaction vessel, a sintering pipe, and a multi-hole orifice plate (or single-hole orifice plate) used as a perforated plate (or single-hole plate) which is mounted at a lower part of a bubble tower.
Also known in the prior art is a perforated plate (or single-hole plate) provided with a collision plate which is mounted immediately on the outflow opening side of gas passages formed in the perforated plate (or single-hole plate).
The aforementioned gas-liquid dispersion device and gas-liquid contact apparatus are also used in wastewater treatment systems for the treatment of water discharged from various facilities. In this kind of application, wastewater is purified by passing it through a wet oxidization process in the presence of molecular oxygen, ozone, or other oxygen source, in which organic substances and inorganic salt components contained in the wastewater are decomposed with or without the aid of a catalyst and converted into harmless substances such as carbon dioxide, water, or nitrogen. What is important in this application is how to uniformly disperse oxygen within a mass of wastewater.
As described above, a multi-hole orifice plate (hereinafter referred to simply as a perforated plate) or a single-hole orifice plate (hereinafter referred to simply as a single-hole plate) having a simple structure is generally used in such a system as a reaction tower in which a liquid or a slurry forms a continuous phase and a gas flows upward as a dispersion device for improving the state of gas-liquid dispersionorgas-liquid contact. The perforated plate issued singly in the reaction tower in certain applications, while a plurality of perforated plates are arranged in equally spaced multiple stages in other applications. In the latter case, the perforated plates would divide the internal space of the reaction tower into a plurality of reaction chambers of the same capacity to allow for a continuous, multi-stage reaction sequence, for instance.
The conventional dispersion device having the simple structure as described above, especially the perforated plate provided at an intake portion, occasionally produces a serious pulsating gas flow, and this may cause such a phenomenon that a fluid passing through the perforated plate does not contain any gas. Another problem which can arise in the conventional dispersion device is that a sufficiently good gas-liquid dispersion state is not accomplished because an even flow of the fluid and gas around the circumference of the perforated plate is not obtained. These problems of prior art technology used to result in a reduction in the efficiency of reaction in chemical reactors, a reduction in the efficiency of absorption in absorption facilities, and a reduction in the efficiency of heat transfer in heat exchangers.
Varying constructions are conventionally known for the gas-liquid contact apparatus and chemical reactors incorporating such a substance as a catalyst. Examples of these constructions are: (i) a first construction in which an empty column is formed beneath a grid for retaining a packed material without filling any substance therein; and (ii) a second construction in which a gas is injected from a gas dispersion device provided at a bottom part of a chemical reactor without injecting the gas and liquid in the form of a mixed-phase flow.
In the first construction mentioned above, the gas and liquid are introduced as a mixed-phase flow from a lower or side portion of a reactor. This construction has a high probability of producing an uneven flow. This is because after the introduction of the gas and liquid into a reactor tower, only the gas may flow in an easy-to-flow direction due to its buoyancy. Such an uneven flow causes an irregular gas-liquid distribution beneath the grid for retaining the packed material. Although the packed material located downstream of gas passages more or less exerts a gas-liquid dispersing effect by itself, it is not sufficient and, therefore, processing performance of the reactor would decline due to deterioration in the state of gas-liquid dispersion and/or gas-liquid contact within the packed material.
If the gas-liquid distribution is irregular immediately beneath the grid for retaining the packed material, it becomes impossible to cause the gas to uniformly act on the packed material. This is because an uneven or pulsating gas flow will be directly supplied to the packed material when the pressure loss caused by the packed material is small, regardless of whether the packed material itself has a certain degree of dispersing effect. If the packed material produces a large pressure loss, it is expected that the dispersion of the gas on the underside of the packed material would be improved to a certain extent. It is however still impossible to produce a really uniform gas flow because there exists unevenness in the density of the packed material itself and its high-porosity portions would produce uneven gas flows.
As is understood from the foregoing, the first construction does not produce sufficient gas dispersion or liquid dispersion, and this may cause unexpected adverse effects, such as deterioration in reaction process performance and side reaction. The impact of the aforementioned problems of this construction would become more apparent if it is taken into account that the reactor of this kind is continuously operated for an extended period of time in most cases and the packed material has its performance limitations. In this construction, uneven gas flows may occur between the perforated plate and the grid for retaining the packed material because of the relatively long distance between them, adversely affecting the performance of the packed material.
If the existence of the gas affects corrosion behavior of the tower, which will occur when oxygen is required for the formation of a passive film on the surface of stainless steel, for instance, the uneven gas flow which prevents normal dispersion of oxygen (or air) will cause a delay in the formation of passive films required for protecting the inner surface of the tower and surfaces of other built-in components. This can eventually destroy existing passive films and accelerate corrosion.
In the gas-liquid contact apparatus according to the second construction mentioned above, the gas dispersion device makes it possible to uniformly introduce a gas into a packed material. However, the gas dispersion device has a complicated structure, and good gas-liquid dispersion is occasionally not obtained directly beneath a grid for retaining the packed material the relatively long distance between the gas dispersion device and grid. Furthermore, since the gas does not exist on the underside of the gas dispersion device or inside a liquid-carrying piping connected to a reactor tower, corrosion within the apparatus may be accelerated. In addition, solid residues tend to deposit at the bottom of the tower. Although this construction is effective when the gas and liquid are separately supplied and only the gas is fed through the gas dispersion device, it is difficult to simultaneously supply the gas and liquid to the gas dispersion device in the form of a mixed-phase flow.
In a multitubular gas-liquid contact reaction apparatus in which heat is exchanged between the inside and outside of pipes, the gas and liquid are usually brought into contact inside the individual pipes. In this apparatus, gas blowoff holes of a gas dispersion device are located just below the individual pipes to uniformly disperse the gas into all the pipes in a manner similar to the second construction described earlier. This arrangement is also associated with a problem that corrosion is likely to occur and solid residues tend to deposit at the bottom in a similar way to what has been described above. Furthermore, since the gas and liquid are separately supplied in the second construction, it is difficult to supply them to the gas-liquid contact apparatus as a mixed-phase flow and obtain uniform dispersion free from the flow pulsation problem.
The gas-liquid contact apparatus is also employed in a wastewater treatment system which is designed to perform wet oxidization wastewater treatment, in which wastewater undergoes an oxidization process in a liquid phase without being condensed in the presence of molecular oxygen, ozone, or other oxygen source. In this case, the temperature of the wastewater is increased (typically 150.degree. C. to 320.degree. C.), the pressure of the wastewater is increased as much as necessary to maintain its liquid phase (typically about 5 to 210 times greater than atmospheric pressure), and then organic substances contained in the wastewater are oxidized. In this application, a sufficiently good dispersion state and treatment efficiency can not be achieved even when a plurality of perforated plates are arranged in a multi-stage structure within an empty-column-type reaction tower. Even when a perforated plate is mounted at the bottom of a catalyst bed in catalytic and wet oxidization wastewater treatment, a high treatment efficiency can not be expected.